It has been common practice for many years to test the strength of an antifreeze solution in the radiator of an automotive type engine by measuring the specific gravity of the solution. By determining the specific gravity of the solution, a conclusion can be reached as to the capability of the solution to withstand freezing at various temperatures.
Such a tester is basically a hydrometer, and such hydrometers have been in common usage for testing the specific gravity of many different liquids such as battery acid, as well as radiator cooling solutions consisting of ethylene glycol and water. Such hydrometers have even been used for testing the potency of alcoholic beverages and mixed drinks.
Such hydrometers, in recent times, have taken the form of a transparent tube into which a sample of the radiator solution is drawn. Oftentimes a short length of flexible rubber hose is attached to one end of the transparent tube, and a rubber bulb is provided on the other end of the tube in order to provide a suction effort for drawing a sample of the radiator solution into the transparent tube. The transparent tube has contained a number of small balls or wafers, each of which has a slightly different specific gravity than each of the other balls in the transparent tube so that by noting the number and identity of the balls in the tube which float, a determination can be made as to the strength and therefore the freeze resistance capacity of the radiator solution.
In the prior art, U.S. Pat. No. 398,726 is illustrative of an early form of such a specific gravity testing device. The glass bubbles of this device are flattened into a somewhat disc-like shape. The transparent tubes also have a flattened cross-sectional shape and generally conform to the flattened shape of the disc-like bubbles. One distinct problem of this type of device is that the glass bubbles tend to get hung up on or stuck to the confronting flattened surfaces of the transparent tube.
U.S. Pat. No. 3,055,220 shows another form of hydrometer having a flattened transparent tube. The disc-like float in this device has small knobs or lugs on the float to maintain a spaced relation between the chamber walls and the flat surfaces of the float.
U.S. Pat. No. 1,768,946 shows flat circular floats confined in an enclosed guideway keeping the floats in proper order.